KR20110095372A - Microporous membrane and method for forming - Google Patents

Abstract

The present invention describes a method of forming a microporous membrane. More specifically, vapor induced phase separation techniques are used to form multizone microporous membranes with improved material throughput.

Description

MICROPOROUS MEMBRANE AND METHOD FOR FORMING

The present invention relates to a method of forming a microporous membrane.

Microporous membranes with various properties are used in many modern products, including articles such as filters, breathable articles, absorbent articles, and medical supplies. Many methods are known for making microporous membranes, including phase separation in the doped layer. By manipulating the conditions that cause phase separation, different morphologies can be generated in the resulting microporous membranes to adapt the membranes to the specific needs of the end user.

One way in which phase separation can occur is to contact a dope formulation with a nonsolvent. Methods for making microporous membranes are described in US Pat. No. 6,736,971 (Sale et al.); 5,869,174 (Wang); No. 6,632,850 (Hughes et al.); 4,992,221 (Malon et al.); 6,596,167 (Ji et al.); 5,510,421 (Dennis et al.); 5,476,665 (Dennison et al.); And US Patent Application Publication No. 2003/0209485; It is further disclosed in 2004/0084364 (Kools).

Condensation of the doped layer with a coagulation bath is described. Another known method for condensation of the dope layer comprises introducing a nonsolvent in the form of a vapor into the dope layer.

The present invention describes a method of forming a microporous membrane. More specifically, vapor induced phase separation techniques are used to form multizone microporous membranes with improved material throughput.

In one aspect, a method of forming a microporous membrane having two or more zones (eg, multiple zones) is provided. The membrane is suitable for applications with high material throughput. The method comprises casting a plurality of dope formulations on a support to provide a multilayer sheet having a first major surface and exposing the multilayer sheet to a first relative humidity level such that water vapor diffuses into the first major surface. Include. The method includes exposing the multilayer sheet to a second relative humidity level higher than the first relative humidity level such that additional water vapor diffuses into the multilayer sheet to cause phase separation to provide a microporous membrane. The method also includes washing and drying the microporous membrane.

In one aspect, a multizone microporous membrane is described that includes a first zone and a second zone. The multi-zone microporous membrane independently comprises pores having an average pore diameter in which the average pore diameter of the first zone is larger than the average pore diameter of the second zone. Multi-zone microporous membranes have water flux measurements of at least 435 lmh / psi (3,000 lmh / psi), first zone pressure peaks below 5 psi and initial bubble points below 10 psi (15 psi). It has forward flow bubble point measurements, including bubble point pressure measurements.

<Figure 1>
1 is a schematic diagram of a method of forming a multizone microporous membrane.
<FIG. 2>
2 is a schematic representation of a multizone microporous membrane.
3,
3 is a schematic diagram of a ternary phase diagram.
<Figure 4>
4 is a SEM micrograph (sectional view) of the multizone microporous membrane of Example 1 having a first zone and a second zone.
Figure 5a
5A is a SEM micrograph (top view) of the first major surface of the first zone of the multizone microporous membrane of FIG. 4.
Figure 5b
FIG. 5B is a SEM micrograph (plan view) of the second major surface of the second zone of the multizone microporous membrane of FIG. 4.
6,
6 is a schematic of a forward flow bubble point graph of the multizone microporous membrane of FIG. 1 (FIG. 4).
<Figure 7>
FIG. 7 is a SEM micrograph (sectional view) of the single zone microporous membrane of Example 4. FIG.
<Figure 8>
8 is a schematic representation of a forward flow bubble point graph of the single zone microporous membrane of FIG. 4 (FIG. 7).

While the invention has been described herein with reference to specific embodiments, it will be readily apparent to one skilled in the art that various modifications, rearrangements, and substitutions can be made without departing from the spirit of the invention. The scope of the invention is therefore limited only by the claims appended hereto.

The term "dope formulation" refers to a composition comprising a polymeric material and an adjuvant in a solvent.

The term "casting" refers to die forming and depositing a dope formulation into layers to form a multilayer sheet.

The term "relative humidity level" refers to the concentration of water vapor in the air and is defined as the ratio of the partial pressure of water vapor in the mixture to the saturated vapor pressure of water at the same temperature. Relative humidity is usually expressed as a percentage.

The term "phase separation" refers to the conversion of a homogeneous system (eg, dope formulation) into two or more phases. Examples of phase separation mechanisms include vapor induced phase separation (VIPS), thermal induced phase separation (TIPS) and liquid-liquid phase separation (LIPS).

The term "adjuvant" refers to additive (s) for the dope formulation.

The term “multi-zone microporous membrane” refers to a membrane having at least two distinct porous portions, each of which is called a “zone” or “microporous zone”.

The description of the numerical range by endpoint includes all numbers contained within that range (eg, 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.8, 4 and 5).

As included in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the content clearly dictates otherwise. Thus, for example, reference to a composition containing "a compound" includes a mixture of two or more compounds. As used in this specification and the appended claims, the term “or” is generally employed in its sense including “and / or” unless the content clearly dictates otherwise.

Unless otherwise indicated, all numbers expressing quantities or ingredients, measurements of properties, etc., as used in this specification and claims, are to be understood as being modified in all instances by the term "about." Accordingly, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification and the appended claims are approximations that may vary depending upon the desired properties sought by those skilled in the art using the teachings of the present invention. At the very least, each numerical parameter should be interpreted at least in terms of the number of significant digits recorded and by the application of ordinary rounding techniques. While the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the embodiments are reported as precisely as possible. However, any numerical value inherently includes an error that inevitably occurs in the standard deviation found in each test measurement.

The present invention forms a microporous membrane using a VIPS process. This process includes casting a dope formulation on a support to provide a multilayer sheet, and exposing the multilayer sheet to water vapor at two different relative humidity levels. The multilayer sheet is first exposed to water vapor at the first relative humidity level. Water vapor diffuses along the first major surface of the multilayer sheet into the multilayer sheet. Without being bound by theory, it is believed that exposure to water vapor at the first relative humidity converts the dope formulation in the multilayer sheet into a metastable state. The multilayer sheet is then exposed to water vapor at a second relative humidity level higher than the first relative humidity level. Water vapor at the second relative humidity level also diffuses into the multilayer sheet, increasing the concentration of water therein and inducing phase separation in the dope formulations. After washing and drying the water-treated multilayer sheet, each of the original layers of the sheet become distinct microporous zones, which are joined to each other along a common interface and together form a multi-zone microporous membrane.

1 is a process flow diagram of forming a microporous membrane by the above method. As shown, the dope formulation is first cast on a support to form a multilayer sheet. The multilayer sheet is then exposed to water vapor at the first relative humidity level and then secondly exposed to water vapor at the second relative humidity level. After exposure to the second relative humidity level, the microporous membrane is typically washed and dried to provide a multizone microporous membrane.

2 illustrates a multizone microporous membrane 200 according to the present invention. Multizone microporous membrane 200 has a first zone 210 and a second zone 220. The first zone 210 and the second zone 220 are coupled to each other along the common interface 230. Both first zone 210 and second zone 220 include a plurality of micropores (not shown) formed as a result of the VIPS process. In an embodiment of the invention, the first zone 210 includes a pore structure having an average pore dimension that is greater than the average pore dimension of the pores in the second zone 220. The first major surface 240 of the first zone 210 is located opposite the common interface 230, and the second major surface 250 of the second zone 220 is formed of the multi-zone microporous membrane 200. Located opposite the common interface 230.

The multizone microporous membrane formed in the present invention is produced without the use of a coagulation bath or from the fabrication of multiple single zone membrane layers. Removal of the coagulation bath reduces the overall costs associated with the formation and transfer of microporous membranes by eliminating the need for filtration and cleaning of such coagulation baths and associated equipment. The resulting multizone microporous membrane has a combination of high material throughput, fast water flow and strong hydrophilicity.

In various embodiments, the dope formulations include polymeric materials, adjuvants, solvents, and additives that control the rate and depth of phase separation across the thickness of the multilayer sheet and affect the formation of specific microstructures in the final multizone microporous membrane. .

The concentration of polymeric material and / or adjuvant of the dope formulation can affect the formation of the final microstructures within each zone, promote the extent to which water vapor diffuses into the multilayer at the first and second relative humidity levels, It can affect the integrity of the microporous membrane. In short, if the concentration of the polymeric material of the dope formulation is too low, no film will be formed. Similarly, if the concentration of the polymeric material of the dope formulation is too high, unwanted or irregular microstructures may be created.

The concentration of polymeric material can be selected, in part, to provide the desired viscosity and / or surface tension for the dope formulation to facilitate casting of the formulation as a layer in a multilayer sheet. Suitable polymeric materials generally include materials that can form micropores (eg, microstructures) upon exposure to water vapor. In some embodiments, the dope formulation comprises a polymeric material having a concentration within the range of about 5% to about 15% by weight, based on the total weight of the dope formulation. In some embodiments, the concentration of polymeric material ranges from about 7% to about 14% by weight or from about 9% to about 14% by weight based on the total weight of the dope formulation.

In the preparation of a membrane made from at least two different dope formulations, namely a first dope formulation and a second dope formulation, the second dope formulation may have a concentration of polymer material that is greater than the concentration of the polymer material in the first dope formulation.

Many polymeric materials are suitable for inclusion in dope formulations, and suitable dope formulations may comprise a single polymeric material or a blend of polymeric materials. The polymeric material can be amorphous, crystalline, or partially crystalline. In some embodiments, the polymeric material in the first dope formulation is the same as the polymeric material in the second dope formulation. In another embodiment, the polymeric material in the first dope formulation is different from the polymeric material in the second dope formulation.

Examples of suitable polymeric materials include, for example, polyethersulfones, polyetherimides, polyimides, polyamides, polysulfones, polyarylsulfones, polyvinyl chlorides, polyethylene terephthalates, polycarbonates, polyolefins, for example , Polyethylene or polypropylene, cellulose esters such as cellulose acetate or cellulose nitrate, polystyrene, acrylic polymers, methacryl polymers, copolymers of acrylic or methacryl polymers, and combinations thereof.

In some embodiments, the polymeric material of the dope formulation is a polyethersulfone according to formula (I).

[Formula I]

In a further embodiment, the polymeric material of the dope formulation is a polyetherimide according to formula (II).

&Lt; RTI ID = 0.0 &

In various embodiments, suitable dope formulations are formulated to have a viscosity high enough to allow the formulation to be cast into a layer in a multilayer sheet. Suitable viscosities for the dope formulations may depend on certain process conditions, such as the actual or expected linear velocity of the substrate supporting the molten dope formulation after the casting step. Similarly, factors such as surface tension, general bead stability, and other fluid properties of the dope formulation are considered to ensure coating uniformity. The aforementioned factors may also affect the diffusion of water vapor into the dope formulation layer according to the VIPS process used in the present invention.

In some embodiments, a suitable viscosity for the dope formulation is in the range of about 2,000 centipoises to about 8,000 centipoises. In some embodiments, the viscosity of the dope formulation ranges from about 2,000 centipoises to about 7,000 centipoises or from about 3,000 centipoises to about 6,500 centipoises.

The dope formulations in the present invention comprise at least one solvent. Suitable solvents are those which dissolve the polymeric material to provide a homogeneous solution. In various embodiments, the solvent is compatible with the polymeric materials, adjuvants and any optional additives present in the dope formulations. The choice of solvent can be made by one skilled in the art to influence the properties of the resulting microporous membrane as well as one or more steps in the VIPS process. For example, the choice of solvent can affect the rate of phase separation for the multilayer sheet, the type of microstructures formed in the finished membrane, or the depth of microstructure formation in the layers of the dope formulations. Examples of solvents for the dope formulations useful in the present invention include, for example, water, dimethyl formamide (DMF), N, N-dimethylacetamide, N-methyl-2-pyrrolidinone (NMP), tetra Methylurea, acetone, methyl ethyl ketone (MEK), methyl acetate, ethyl acetate and other alkyl acetates, dimethylsulfoxide (DMSO), and combinations thereof. In some embodiments utilizing a polyethersulfone polymer, the solvent is N-methyl-2-pyrrolidinone. The solvent can be oligomeric or polymeric character. In some embodiments, the dope formulation may comprise more than one solvent or blend of solvents.

The solvent provides a stable homogeneous solution for casting the dope formulation to form a microporous membrane. Solvents are classified into 'good' solvents, 'non-solvent', and 'inferior' solvents, depending on their ability to dissolve the selected polymer therein. Solvents classified as 'excellent' are those in which the interaction (gravitation) between the polymer molecule and the solvent molecule is greater than the attractive force between the polymer molecules. The converse is true for nonsolvents. Solvents described as 'inferior' are those in which the interaction between the polymer and the solvent is such an attractive force between the polymer molecules.

In one embodiment, a stable homogeneous dope formulation can be obtained by first dissolving the selected polymer in a good solvent. For dope formulations with polymeric materials in the form of polyethersulfones, suitable 'good' solvents include, for example, N-methyl-2-pyrrolidinone, dimethylacetamide, dioxane, dimethylsulfoxide, chloroform, tetramethylurea , And tetrachloroethane. In general, good solvents can dissolve significant amounts of polymeric material. In some embodiments, the 'good' solvent is one that is miscible with the polymeric material at a polymer concentration of at least about 5 weight percent based on the total weight of the dope formulation.

One useful way to evaluate solvents for compatibility with polymers is to use Hildebrand solubility parameters. These parameters refer to solubility parameters represented by the square root of the cohesive energy density of the material, which has units of (pressure) ^1/2 ,

(ΔH-RT) equal to the ^1/2 V ^1/2,

here,

ΔH is the molar vaporization enthalpy of the material,

R is the universal gas constant,

T is the absolute temperature,

V is the molar volume of the solvent.

Hildebrand solubility parameters are described in Barton, AFM, "Handbook of Solubility and Other Cohesion Parameters", 2 ^nd Ed., CRC Press, Boca Raton, Fla. (1991) for solvents; "Polymer Handbook", 4 ^th Ed., J. Brandrup & EH Immergut, Eds. John Wiley, NY, pp. VII 675-714 (1999) for monomers and representative polymers; And Barton, AFM, "Handbook of Polymer-Liquid Interaction Parameters and Solubility Parameters", CRC Press, Boca Raton, Fla. (1990) are tabulated for a number of commercially available polymers.

Adjuvants selected for the dope formulations are generally soluble in the solvent and compatible with the polymeric material. Adjuvants may be added to the dope formulations to control the viscosity of the dope formulations before casting them into layers in the multilayer sheet. Similarly, the concentration of the adjuvant in the dope formulation can affect the diffusion of water vapor into the layer of the dope formulation during the VIPS process. Adjuvants may also be added to the dope formulations to control the rate (kinetics) of phase separation in the VIPS process. Some useful auxiliaries include, for example, poly (alkylene) glycols, polyethers or combinations thereof. In some embodiments, the adjuvant is poly (ethylene) glycol.

Adjuvants added to the dope formulation at a selected concentration may cause phase separation at a predetermined depth within the layer of the dope formulation. In some embodiments, the depth of phase separation in the layer of the dope formulation ranges from about 5% to about 100% of the thickness of the layer.

In some embodiments, the concentration of the adjuvant (s) in the plurality of dope formulations is selected to affect phase separation and provide different pore size distributions and different porosities for each different zone in the multizone microporous membrane. Multizone microporous membranes with zones with different average pore diameters are useful in certain high material throughput and high flux filtration applications.

In some embodiments, the adjuvant concentration in the dope formulation may range from about 60% to about 70% by weight based on the total weight of the dope formulation. In some embodiments, the concentration of the adjuvant is in the range of about 60% to about 68% by weight or about 62% to about 68% by weight based on the total weight of the dope formulation.

In the preparation of multizone microporous membranes using the VIPS process, the dope formulation is first cast on a support to provide a multilayer sheet. The support may be a plastic or metal sheet and may be continuous or discontinuous (eg, discrete). The selected support provides stability for the laminated layers of the dope formulation during casting and during transport through the first and second humidified environments, and during the washing and drying steps.

A plurality of dope formulations is typically cast to form a multilayer sheet on a support. In this configuration, the first dope formulation layer is laminated on the second dope formulation layer, and an interface is formed between these layers. The second dope formulation layer is disposed directly on the support and the first dope formulation layer is positioned on top of the second dope formulation on the opposite side of the support. The resulting multilayer sheet has a first major surface that coincides with the exposed surface on the first dope formulation layer.

In some embodiments, two dope formulation layers are cast simultaneously to provide the aforementioned configuration. Simultaneous casting of multiple dope formulations can be accomplished using any of a number of known techniques and devices. Some useful devices are known in the art for multipath applicators, dual-knife over roll devices, dual layer slot fed knife dies, and doping formulation castings. Other related devices.

The thickness of any dope formulation layer depends on several variables, as known to those skilled in the art. For example, the thickness of the layer may depend on the equipment settings and the rheology and viscosity of each dope formulation. In addition, the aforementioned casting methods typically require the use of a die to shape the dope formulation when the dope formulation is cast into a multilayer sheet. As a result, the thickness of the dope formulation layer is directly influenced by the gap dimension of the particular die slot used for the casting operation. Moreover, the gap dimension can be adjusted, in part, to adjust the viscosity of the dope formulation. When casting a dope formulation using a double knife over roll apparatus, the gap dimension may range from about 150 micrometers to about 300 micrometers.

After casting the dope formulation layer to form a multilayer sheet, the multilayer sheet is exposed to at least two humidification environments to cause phase separation and microstructure formation within the layered dope formulation layer.

The design of a dope formulation suitable for forming a microporous membrane is better understood in view of the principles of polymer solubility, miscibility of components, and concentrations of polymers, solvents and water. At certain concentrations, the polymeric material is completely miscible with the solvent. At other concentrations, there is a phase separation zone.

Referring to FIG. 3, a ternary state diagram 300 is shown for the components of the exemplary dope formulation, namely polymer concentration, water concentration and solvent concentration. 3 illustrates the relationship between the three components. In state diagram 300, a binodal curve 305 depicts regions 320 and 330. Each region represents a region of component concentration for the dope formulation, where region 320 represents a thermodynamically stable concentration of the components and region 330 represents a thermodynamically unstable concentration of the component. Thus, the relationship of polymer concentration to solvent and water concentration is described by the binodal curve 305. Region 330 is further divided to include region 340 between spinodal curve 310 and binodal curve 305. Spinoidal curve 310 and binodal curve 305 intersect at point 315 representing the so-called theta state Θ. Without being bound by theory, in Θ, the interaction force between the polymer material molecule and the solvent molecule is equal to the interaction force of the polymer molecule with respect to other molecules of the same polymer. Doped formulations with component concentrations in region 340 represent compositions that are considered metastable prior to phase separation. Doped formulations with component concentrations within region 330 but outside region 340 represent phase separated compositions.

In the treatment of dope formulations via the VIPS process, the formulations are exposed to water vapor to increase the moisture content of the formulations and thereby change the concentrations of solvents and polymers. The VIPS process adds water (eg, as water vapor) to the dope formulation and the component concentration of the formulation is from region 320, wherein the formulation is thermodynamically stable (eg, solution). It is intended to cause phase separation of the homogeneous solution by varying the component concentration until the formulation is believed to be metastable. With at least one additional exposure to water vapor at a second relative humidity level, a sufficient amount of water vapor diffuses into the dope formulation to further move the formulation into the region 330 where the component concentration of the formulation emerges from the region 340 where phase separation occurs. I will.

A humidifying environment (ie, chamber or station) can be used to deliver water vapor to the dope formulation of the multilayer sheet. For example, water vapor can be delivered by injecting steam into the humidification chamber. Sensors located within the chamber can be used to monitor actual air temperature and relative humidity percentages (eg, relative humidity levels). The exposure time to water vapor can vary within a useful range depending on factors such as the relative humidity level used, air temperature and gas phase (eg steam) velocity. In various embodiments, the exposure time for the multilayer sheet can range from about 7.5 minutes to about 25 minutes, for example. In some embodiments, the exposure time may be, for example, in the range of about 10 minutes to about 22.5 minutes, in the range of about 10 minutes to about 20 minutes, or in the range of about 12.5 minutes to about 20 minutes.

When delivering water vapor to a dope formulation consisting of a polymer and a solvent described herein, the first relative humidity level can range from about 45% to about 55%. In some embodiments, the first relative humidity level can range from about 46% to about 54%, from about 46% to about 53%, or from about 46% to about 52%. After being exposed to water vapor at the first humidity level for a period of time, the multilayer sheet is exposed to the second relative humidity level to induce phase separation. The second relative humidity level is at least 5% greater than the first relative humidity level. In some embodiments, the second relative humidity level is at least 6% greater, at least 7% greater, at least 8% greater, at least 9% greater, or at least 10% greater than the first relative humidity level. . The second relative humidity level can range from about 60% to about 80%. In some embodiments, the second relative humidity level can range from about 60% to about 75%, from about 62% to about 75%, or from about 65% to about 75%.

In some embodiments, the dope formulation in the multilayer sheet is exposed to moisture at a relative humidity level intermediate to the first and second relative humidity levels. Medium relative humidity levels may be required for certain dope formulations or under certain processing conditions in order to gradually increase the moisture content of the dope formulations. In one embodiment, the first relative humidity level can range from about 45% to 50%, the median relative humidity level (eg, medium) can range from about 50% to 55%, and the second relative humidity level May range from about 55% to 65%.

The humidification environment used for the delivery of water vapor and the aforementioned relative humidity levels is typically maintained within the desired temperature range of about 15 ° C to about 55 ° C. In some embodiments, the temperature can be, for example, about 20 ° C to about 50 ° C, about 20 ° C to about 47 ° C, or about 20 ° C to about 45 ° C.

After exposure to water vapor, the resulting phase separated microporous membrane is washed and dried. Washing the microporous membrane assists in the removal of the solvents (including water) used in the dope formulations. The disclosed washing step helps to prevent the microstructure of the membrane from collapsing. Washing can be accomplished by spraying, dipping and other techniques for removing the solvent and water. In one embodiment, the membrane moves through a tank having a fluid retention roller. After washing, the microporous membrane can be dried by convection, air drying and vacuum treatment. In some embodiments, the membrane is dried at ambient conditions in air.

The effective pore size (eg, average pore diameter) formed in the multizone microporous membrane can range from about 0.05 micrometers to about 2 micrometers. In some embodiments, the pore dimensions from the microporous membrane can be, for example, in the range of about 0.1 micrometers to about 1.5 micrometers or in the range of about 0.2 micrometers to about 0.8 micrometers. In some embodiments, the pore dimensions of the microporous membrane can be nearly uniform or symmetrical over the thickness of one or more regions of the zone. The zones may have a symmetrical distribution of pores extending through a portion of the thickness of the zone or through the entire thickness of the zone. In some embodiments, the multizone microporous membrane formed by the described method includes at least two zones with nearly symmetrical pore distributions extending through the thickness of their respective zones.

The pore size of the membrane refers to the average diameter of the openings in the microstructures formed during phase separation. Pore size can be measured, for example, by the bubble point pressure method. Some other pore size and pore size distribution measurement methods may include, for example, solute retention, and flow / pressure techniques. Pore diameters can also be estimated by porometry analysis and by separate measurement of bubble points, with higher bubble points representing denser or smaller pores.

Multizone microporous membranes may be formed comprising at least two zones with different pore dimensions within their respective zones.

The microporous membrane formed by the method described herein provides a multizone microporous membrane having a first zone and a second zone. The pores in the first zone provide a first microstructure having a larger pore dimension than the pores formed in the second zone providing the second microstructure.

The microstructures formed may depend on the dope formulation and the processing parameters. The first and second microstructures can provide a continuous or discontinuous path through the membrane. The formation of the microstructures may depend on the concentration and water vapor concentration of some of the components of the dope formulations (eg, polymeric materials, coating aids, nonsolvents). The shape (eg symmetric or asymmetric) of the microstructures may further depend on the metering (eg layer thickness), relative humidity level and / or rate of phase separation of the dope formulation. The form may also depend on the phase separation mechanism and the associated pressure and temperature processing conditions.

In some embodiments, the first zone of the microporous membrane has an average pore dimension that is greater than the average pore dimension of the second zone. The ratio of the average pore size of the first zone to the average pore size of the second zone can be, for example, in the range of about 10: 1 to about 2: 1.

The thickness of the microporous membrane formed may depend on the thickness of the dope formulation layer when cast and subsequent solvent removal and subsequent washing and drying steps of the microporous membrane. In some embodiments, the thickness of the microporous membrane can be, for example, in a range from about 125 micrometers to about 150 micrometers. In some embodiments, the thickness of the microporous membrane may range from about 125 micrometers to about 145 micrometers, from about 125 micrometers to about 140 micrometers, or from about 125 micrometers to about 135 micrometers.

In one embodiment, the thickness of the first zone is greater than the thickness of the second zone of the multizone microporous membrane. In another embodiment, the thickness of the first zone is the same as the thickness of the second zone of the multizone microporous membrane.

Multizone microporous membranes formed by the process of the invention can be used in filtration applications. For example, the first zone can act as a pre-filter to capture large particles, and the second zone can capture small particles.

Multizone microporous membranes comprising a first zone and a second zone comprise pores having an average pore diameter. The average pore diameter of the first zone is generally greater than the average pore diameter of the second zone.

In one aspect, the multizone microporous membrane formed in the present invention has a permeation flow rate measurement of at least 435 lmh / psi (3,000 lmh / psi) and a first zone pressure peak of less than 3 psi (5 psi) and less than 15 psi (103.4 psi). Has a forward flow bubble point measurement comprising an initial bubble point pressure measurement.

In some embodiments, the combined microporous membrane can be formed including the previously described multizone microporous membrane, laminated to a single zone microporous membrane. As used herein, the term “single zone microporous membrane” refers to a microporous membrane having at least one porous zone resulting from bubble induced phase separation of a single dope formulation. In some embodiments, a single zone membrane may have more than one layer, but the resulting membrane zones will have substantially the same average pore diameter. Such single zone membranes are prepared in the same manner as described herein for multizone microporous membranes, but using the same or at least substantially the same first and second dope formulations. Single zone membranes comprise two 'zones', both of which have the same shape and average pore size, resulting in a single filtration zone.

Lamination of the multi-zone microporous membrane and the single-zone microporous membrane may be accomplished using known lamination techniques, including pressurization or heating methods, and / or using suitable additives or adhesives. The resulting article is called a combined microporous membrane consisting of a multilayer microporous membrane in which a single zone membrane is fixed (eg, laminated) to the major surface of the second zone.

Multizone membranes formed in the present invention do not require a combined membrane formed by lamination of at least two membranes. The microporous membrane formed by the described method can reduce manufacturing costs and increase manufacturing efficiency. Using a humidifying environment to deliver water vapor to the sheets to cause phase separation in the multilayer sheet eliminates the need for coagulation baths and multiple cleaning steps.

The multizone microporous membranes disclosed herein have a high material throughput. Multizone microporous membranes can be used in pharmaceutical, biological, medical, food and beverage applications. Filter assemblies comprising a cartridge, an inlet, an outlet, and a multizone microporous membrane located within the cartridge can be used for residential, commercial, and industrial use.

The invention will be further clarified by the following non-limiting examples.

Example

Unless otherwise noted, all parts, percentages, and ratios reported in the following examples are weight based, and all reactants used in the examples are obtained from, or available from, the chemical suppliers described below. It can be synthesized by conventional techniques.

Initial Bubble Point Pressure (IBP)-ASTM Standard E-128-99 (2005). IBP measurements were recorded on a 47 mm diameter pre-wet microporous membrane with fluorine compound FC-43 (Sigma-Aldrich, St. Louis, MO).

Water Flow Rate (WFR)-WFR measurements were recorded on the microporous membrane. This membrane was pre-wet with isopropanol and deionized water. The length of time required for 100 mL of deionized water to pass through the microporous membrane under reduced pressure (59 cm Hg) was recorded. WRF methods are further described in US Pat. Nos. 7,125,603 and 6,878,419 (Mekela et al.), Incorporated herein by reference.

Robust Molasses Throughput (RMT)-RMT measurements are based on a multistation stand (e.g., B & G Foods, Incorporated, Parsippany, NJ) For example, in multiple sample stations for conducting several experiments simultaneously under the same process conditions. The molasses solution was pumped through a 47 mm diameter microporous membrane disk at a constant volumetric flow rate of 48 ml / min. The microporous membrane was pre-wet with a solution blend of 60 wt.% Isopropanol / 40 wt.% Deionized water. The accumulation volume (ml) of the filtrate was taken when a trans-membrane pressure of 172 kPa (25 psi (lb / square inch)) was achieved.

Forward Flow Bubble Point (FFBP) —FFBP measurements were recorded using a 47 mm diameter membrane prewet with an isopropanol / deionized water (60/40 vol./vol.) Mixture. For multizone microporous membranes, the first zone pressure peak and initial bubble point pressure measurements were recorded. FFBP measurements are similarly described in US Pat. No. 4,341,480 (Pall et al.), US Pat. No. 6,413,070 (Meyering et al.), And US Pat. No. 6,994,789 (Sale et al.).

Comparative Example 1 and Comparative Example 2 (CE1 and CE2)

Commercial two-layer membranes with gradient form were investigated: CE1-sterile high dose (SHC) (Millipore, Billerica, Mass.), And CE2-DuraPES TM-600 (Germany Wuppertal). Membrana).

Example 1

Doped formulations were prepared and delivered to the double-knife rollover device. The first doping formulation (first doping) was 1-methyl-2-pyrrolidinone (NMP; Sigma-Aldrich, St. Louis, MO) / polyethylene glycol (PEG-400, (Sigma-Aldrich, St. Louis, MO) 9.7 wt.% Polyethersulfone (Radel H-2000P; Solvay, Alpharetta, GA) dissolved in a solution blend (27.3 / 63 wt.%) The second dope formulation (eg, the second dope) is 14 wt. Dissolved in a solution blend (17/69 wt%) of 1-methyl-2-pyrrolidinone (NMP) / polyethylene glycol (PEG-400). % Polyethersulfone (Sigma-Aldrich, St. Louis, Missouri).

125 micrometer-thick polyethylene terephthalate (PET) film (3M Company, St. Paul, Minn.) Conveying the first and second dope formulations at a linear speed of 0.41 meters / minute (m / min) Co-cast onto the bed. The gap dimension of the double knife over roll apparatus was set to 150 micrometers for the second dope formulation and the gap dimension to 225 micrometers for the first dope formulation. The viscosity of the first and second dope formulations was 3,000 centipoise (cp) and 7,500 cp, respectively. The first and second dope formulations were cast as nested layers forming an interface between these two formulations to provide a multilayer sheet.

The multilayer sheet was introduced into a 7.31 meter long air-floating dryer line with first and second humidified environmental chambers and wash and dry sections. Each of the first and second humidified environmental chambers was approximately 2.45 m in length. Steam was injected into the chamber to achieve first and second relative humidity levels. The relative humidity of the humidification chamber was controlled by a needle valve located downstream of the steam injector. A humidity sensor was used to monitor the actual temperature and relative humidity in the chamber. The multilayer sheet was exposed to a first relative humidity level of 56% at 45 ° C. in a first humidification chamber to allow water vapor to diffuse into the first major surface. The multilayer sheet was then exposed to a second relative humidity level of 65% at 43.3 ° C. in a second humidification chamber to cause phase separation. The resulting article was washed and dried to provide a multizone microporous membrane.

4 is a SEM micrograph showing in cross section the microporous structure of the multizone microporous membrane 400 according to Example 1. FIG. Multizone microporous membrane 400 includes two separate zones having two distinct pore sizes. The first zone 405 has a pore size of about 0.6 micrometers and the second zone 410 has a pore size of about 0.2 micrometers separated by the interface 415. The first zone 405 of the multizone microporous membrane 400 can provide pretreatment filtration membrane characteristics, and the second zone 410 can provide sterile membrane characteristics, for example, in high throughput filtration applications.

FIG. 5A is an SEM micrograph (top view) illustrating a first major surface of the first zone 405 of FIG. 4. FIG. 5B is an SEM micrograph (top view) illustrating a second major surface of the second zone 410 of FIG. 4.

The FFBP curve for Example 1 is illustrated in FIG. 6. This curve demonstrates a multizone morphology with a first zone and a second zone. In FIG. 6, the first zone pressure peak appears at about 27.5 kPa (4 psi) when nitrogen cleans the first zone. Bulk flow at about 11.34 psi indicates that the appropriate nitrogen pressure has been reached to clean the second zone of the multizone microporous membrane. The test results from Example 1 are shown in Table 1.

Example 2

Multizone microporous membranes were formed in a manner similar to Example 1, with the following exceptions: Polyethersulfone polymer (Ultrson E-6020; BASF, position) was prepared with first and second dope formulations. Used for; The first humidity level was 50% at 45 ° C. and the second humidity level was 65% at 43 ° C. The resulting FFBP profile (not shown) demonstrated a multizone morphology with a first zone pressure peak of 31 psi (4.5 psi). The test results from Example 2 are shown in Table 1.

Example 3

Multizone microporous membranes were formed in a manner similar to Example 1 with the following exceptions: The gap dimension of the double knife over roll apparatus for delivering the first doped layer was set to 350 micrometers; The gap dimension for delivering the second doped layer was set to 125 micrometers; The first relative humidity level was 48% at 47.2 ° C .; The second relative humidity level was 70% at 45.6 ° C. The resulting FFBP profile (not shown) demonstrated a multizone morphology with a first zone pressure peak of 31 psi (4.5 psi). The test results from Example 3 are shown in Table 1.

Example 4

Monolayer single zone microporous membranes (sterile grade membranes) were prepared for use in the fabrication of the combined membranes. Single zone microporous membranes were formed using the double knife over roll apparatus of Example 1. The second dope formulation of Example 2 was cast and exposed to a first relative humidity level of 43% at 45 ° C. The single dope formulation layer was then exposed to a second relative humidity level of 65% at 43.3 ° C. The resulting material was washed and dried.

7 is a SEM micrograph of the cross section of a single zone microporous membrane, showing symmetrical morphology through the entire thickness of the single zone microporous membrane.

The FFBP curve for Example 4 is illustrated in FIG. 8. This curve demonstrates a single zone morphology. In FIG. 8, nitrogen (g) washes a single zone at a peak of about 241.3 kPa (35 psi). Single zone microporous membranes were tested and the results are illustrated in Table 1.

The single zone microporous membrane of FIG. 7 can be applied to (eg, laminated) a multizone microporous membrane to form a combined microporous membrane. The combined microporous membrane can have a single zone membrane (first layer) as a sterile membrane and a multizone microporous membrane (second layer) that functions as a pretreatment filtration membrane.

Various modifications and variations of the present invention will be apparent to those skilled in the art without departing from the scope and spirit of the invention, and it should be understood that the invention is not limited to the exemplary elements described herein.

Claims (20)

Casting a plurality of dope formulations on a support to provide a multilayer sheet having a first major surface;
Exposing the multilayer sheet to a first relative humidity level such that water vapor diffuses into the first major surface;
Exposing the multilayer sheet to a second relative humidity level higher than the first relative humidity level such that additional water vapor diffuses into the multilayer sheet, causing phase separation to provide a microporous membrane;
Washing the microporous membrane; And
Drying the microporous membrane
Method for forming a microporous membrane comprising a. The method of claim 1, wherein casting the plurality of dope formulations comprises casting the first and second dope formulations to provide a multilayer sheet. The method of claim 2, wherein the first dope formulation is the same formulation as the second dope formulation. The method of claim 1, further comprising formulating a plurality of dope formulations each comprising a polymeric material, an adjuvant, and a solvent. The method of claim 4, wherein the polymer material in each of the plurality of dope formulations is polyethersulfone, polyetherimide, nylon, polyimide, polyamide, polysulfone, polyarylsulfone, polyvinyl chloride, polyalkylene terephthalate , Polycarbonates, polyolefins, cellulosic materials, polystyrenes, acrylic polymers, methacryl polymers, copolymers of acrylic or methacryl polymers, and combinations thereof. The method of claim 4, wherein the adjuvant comprises poly (alkylene glycol), polyether, or a combination thereof. The method of claim 6, wherein the poly (alkylene glycol) is poly (ethylene glycol). The method of claim 4, wherein the concentration of the adjuvant of the first and second dope formulations independently ranges from about 60 to about 70 weight percent based on the total weight of the dope formulation. The method of claim 4, wherein the concentration of polymeric material of the second dope formulation is greater than the concentration of polymeric material of the first dope formulation. The method of claim 4, wherein the concentration of polymeric material of the first and second dope formulations independently ranges from about 5 to about 15 weight percent based on the total weight of the dope formulation. The method of claim 1, wherein the second relative humidity level is at least 5% greater than the first relative humidity level. The method of claim 11, wherein the first relative humidity level ranges from about 45 to about 55% and the second relative humidity level ranges from about 60 to about 80%. The method of claim 1, wherein exposing the multilayer sheet further comprises exposing the multilayer sheet to intermediate humidity levels. The method of claim 13, wherein the intermediate humidity level is halfway between the first relative humidity level and the second relative humidity level. At least 435 lmh / psi (3,000 lmh / psi) comprising at least 435 lmh / cc (3,000 lmh / psi), the first and second zones independently comprising pores having an average pore diameter greater than the average pore diameter of the second zone; Flow forward measurement, including water flux measurements of &lt; RTI ID = 0.0 &gt; and &lt; / RTI &gt; a first zone pressure peak of less than 5 psi and an initial bubble point pressure measurement of less than 10 psi. multi-zone microporous membrane with flow bubble point measurements. The multizone microporous membrane of claim 15, wherein the first zone has a first thickness and the second zone has a second thickness, wherein the first thickness is greater than the second thickness. The multizone microporous membrane of claim 15, wherein the first zone has an average pore diameter in the range of about 0.5 micrometers to about 0.7 micrometers, and the second zone has an average pore diameter in the range of about 0.1 micrometers to about 0.3 micrometers. . The multizone microporous membrane of claim 15, wherein the first and second zones independently have symmetrical morphology. The multi-zone microporous membrane of claim 15 laminated to a single-zone microporous membrane, wherein the single-zone microporous membrane is laminated adjacent to the second zone and the average pore diameter of the single-zone microporous membrane is greater than the average pore diameter of the second zone. Small combined microporous membrane. A filter assembly comprising a cartridge having an inlet and an outlet, and the multi-zone microporous membrane of claim 15 located within the cartridge.

Images